weight carbohydrates resulting from combinations of two or more mono- 

 saccharides (disaccharides, trisaccharides) are called oligosaccharides. 

 The individual sugar units making up an oligosaccharide are bound to- 

 gether by glycosidic linkages (Formula (2-9) ). Polysaccharides are high 

 molecular weight carbohydrates composed of many monosaccharide re- 

 peating units which are also linked to one another by means of glycosidic 

 bonds. Many of the polysaccharides yield glucose as the end product 

 following complete hydrolysis (e.g., cellulose, starch, glycogen). 



1,4-a linkage 



6 



CH20H 



5| 



OH H OH 



a-Maltose 



Carbohydrate, which is synthesized in the presence of light through 

 the intermediacy of chlorophyll in green plants (see Figure 3-17), is a 

 universal constituent of all living cells. It is one of the primary sources 

 of energy for maintenance of cellular activity (see Chapter 3, Figures 

 3-9 and 3-11). The relative efficiency of carbohydrates in promoting 

 cell function is due to the cell's ability to phosphorylate available carbo- 

 hydrate and to partially degrade this phosphorylated product before it is 

 finally broken down to CO2 and HoO by the oxidative mechanisms of the 

 cell. In addition to its role as an energy source, carbohydrate in the 

 polymerized form is an important constituent of certain cell structures. 

 For example, cellulose is an integral component of plant cell walls, 

 while chitin constitutes the major part of the exoskeleton of insects and 

 crustaceans. 



Inorganic Cons+i+uents 



Besides being complexed with organic molecules, many inorganic salts 

 occur free and in the ionized state. The relationship between various in- 

 organic salts and between the salts and organic constituents is extremely 

 complex. In general, it is presumed that they provide the necessary ionic 

 balance for a variety of physiological processes. Almost every element 

 in the periodic table can be shown to play some relatively important 

 role in the living organism. The divalent calcium (Ca+ + ) ion appears 

 to be essential in maintaining the integrity of many cell structures. Mag- 



22 / CHAPTER 2 



